Closure cap with a seal and method of and apparatus for forming such closure and seal

ABSTRACT

In combination, a container and a linerless cap and a method of forming the cap. In the method the cap is molded from plastic and includes a top wall, an outer depending skirt and an internal depending substantially annular wall having an upper end integral with and depending from the top wall and a lower free end. Thereafter the free end is engaged by a curling tool to progressively turn the free end away from the internal wall to curve the free end into a curvilinear compressible and resilient free end adapted to be engaged for sealing. The engageable free end of the seal can have a coil, O, U, J or quarter round cross sectional shape and can be a rim, plug or corner seal.

This is a divisional application of application Ser. No. 07/061,304,filed Jun. 10, 1987, now U.S. Pat. No. 4,872,304, which is acontinuation-in-part application of Ser. No. 06/809,057, filed Dec. 12,1985, now U.S. Pat. No. 4,709,824, which is a continuation-in-partapplication of Ser. No. 06/809,058, filed Dec. 12, 1985, now U.S. Pat.No. 4,708,255.

FIELD OF THE INVENTION

This invention relates to a closure cap with a seal in combination witha container and to a method of and apparatus for forming the closure andseal.

BACKGROUND OF THE INVENTION

The function of a closure cap to adequately seal the contents of acontainer against leakage from or into the container traditionally hasbeen met by incorporating a soft liner to effect a seal between theunder portion of the cap lid and the upper face of the bottle neck rim.The liner may be preformed from sheet or formed in place and is producedfrom materials or laminar combinations or materials which provide easycold formability to enable the liner to conform to the individualconfiguration of the neck rim, including manufacturing aberrations anddefects. Because of the specialized sealing function of a liner, it istypically made from softer polymers than those selected to perform themore structural cap functions of providing a strong resilient enclosurefor the neck opening with a strong mechanical engagement therewith. Insome instances stiffer and stronger polymers, including some which aresuitable for producing threaded caps, may be foamed to produce anexpanded, less dense sheet having a softer, more flexible characteristicand liners may be made therefrom.

An important characteristic sought for liners and not generally met,especially by plastic caps where the cap lid geometry and dimensions maybe affected in time by internal pressure and/or heat exposure, is theability to adjust to such dimensional changes without undue loss ofsealing pressure. This calls for a liner with a high level of resilienceand resistance to cold flow, particularly for carbonated and/orpasteurized foods and beverages employing plastic caps, to offset thelarge amounts of cold flow or creep which can result in a dome shapelid. Most soft, conformable liners by their nature will cold flow toadapt to the initial cap geometry but do not have the elasticity orresilience to adapt to such changing cap geometry and can lose theirsealing engagement. An ideal liner, therefore, would possess a soft,easily conformable sealing surface, backed by a resilient supportingstructure having good resistance to plastic creep to assure a goodsealing engagement at all times under all conditions. Such an idealliner could be vulcanized rubber which can possess both softness andresiliency over long time periods. However, the cost of such sealsprecludes their use in most applications. On the other hand, plasticswhich are suitably soft exhibit poor long term creep resistance andresilience. An alternative approach in popular use is a laminate of aspringy paperboard substrate with a soft conformable sealing surfacesuch as wax or plastic. However, this approach has significantperformance limitations especially when moisture is present.

In any event, all cap liners add another component to the closure andsignificantly add to its cost.

Because of an economic advantage, attention has been devoted in recentyears to developing caps which have an integral, "linerless" seal. Theavailability of such semi-rigid plastics as polypropylene andpolyethylene, which combine a moderate level of strength and resiliencewith a moderate level of softness and conformability, has made possiblepopular use of caps with linerless seals. Typically, such caps employ acircular flange under the cap lid having a wedge shape cross section thelower corner of which is thin and flexible and intended to abut the topsurface of the bottle neck rim in a compressive action for sealing. Thewedge shape flange generally is vertical and provides a sealing arearestricted to the width of the narrow, more flexible portion of thewedge shape. For their effective use, they depend upon a very high levelof sealing force on a very limited sealing area which makes themsusceptible to sealing surface imperfections, wide dimensionalvariations in container necks and the decay of sealing force over longtime periods.

Other linerless caps employ conical flanges which present an angularcross section from the vertical so that capping will cause the flangesto flex and slide out over the top surface of the neck rim therebycreating a somewhat larger sealing area than obtainable with verticalflanges in straight compression. While the larger, though still limitedsealing area has positive advantages, this is offset by the fact thatthe sealing pressure is at the same time reduced proportionately to theincrease in sealing area and they too perform poorly with containernecks having wide dimensional variations. Another important limitationof such conical linerless features is the difficulty of removing suchfeatures from an injection mold. This results in more complex and costlymold construction and operation and also excludes the more rigidplastics from use.

Some other linerless caps employ conical flanges which engage thecorners of the neck rim with the underside of the flange. Such featuresrely on the use of very high sealing pressure directed against arestricted line contact at the rim corners to obtain sealing integrity.In such cases, sealing integrity depends on container rim corners whichare without blemishes as produced and which, because they are mostsusceptible to marring during handling, are suitably protected from suchbefore they are capped and sealed. Also, to the extent that the conicalflanges approach the shape of a cylinder, their sealing integrity issignificantly affected by out-of-round or other common dimensionalvariations of the container manufacturing process or variations betweenmanufacturers resulting from the fact that inside neck dimensionstypically are not specified. And to the extent that the flanges becomemore conical, more complex and costly mold constructions and operationresult.

Still another type of linerless cap employs a plug configuration insealing contact with the inside wall of the container neck. This type ofseal has the advantage of engaging that surface of the bottle neck whichmay be freest from manufacturing defects and most protected fromincidental marring in handling thereafter. However, wide manufacturingdimensional tolerances and the industry-wide practice of not specifyingthe neck bore dimension impose severe limitations in trying to obtainconsistent sealing engagement and integrity. As a result, resistance totapered plug seals can push the cap lid up to varying degrees ofundesirable dome shapes. Or such plug seals can yield unacceptably widevariations in sealing engagement and pressures. Efforts to overcome suchdeficiencies have led to proposed designs with flanges extendingradially from generally cylindrical plugs wherein the outer rim of theflange makes a narrow sealing contact with the neck bore and issupported by a hinged flexing action. (See, for example, U.S. Pat. Nos.4,090,631, 4,016,996 and 4,210,251). An additional problem has beenencountered with this type of linerless seal in that the lip or rim ofthe flange may be distorted by the neck rim during capping leading toimperfect seals. Efforts to eliminate this problem can introduce otherproblems specific to pressurized containers wherein blow-off ormissiling of the caps can occur during uncapping. Another effort toavoid distortion of the lip or rim of such a seal is a cap design andmethod of producing it wherein a radially extending flange having adownward orientation as molded is hingedly "bent", "folded" or invertedinto an upward orientation before it is applied to the container. (SeeU.S. Pat. No. 4,210,251 and British Patent No. 1,024,762). This isaccomplished with extra mold portions and actions during part removal orsubsequently in an appropriate fixture to hingedly invert the flange.This effort, therefore, requires the molding of a seal of complex shapeutilizing a complicated and costly mold construction and moldingoperations followed by inverting the sealing portion of the sealhingedly to alter its orientation but not its shape.

Importantly in all cases an inherent limitation to heretofore availablelinerless caps is that the sealing surface has the same plastic in thesame physical state as the structural portion of the cap. This hascalled for a compromise in the softness and conformability of thesealing surface or in the strength of the structural cap portions, ormost frequently both, with consequent limitations in the cap usefulness.That is, to achieve a softer more conformable seal, poorer threadstrength must be accepted or to achieve greater thread strength, aharder, less conformable seal must be accepted.

Thus, known caps with linerless seals are beset with drawbacks andproblems associated with their need to perform with container neckshaving imperfect sealing surfaces and wide dimensional tolerances; theirlimited sealing integrity based on restricted sealing area and loss ofsealing pressure over extended periods of time especially at elevatedtemperatures or with internal pressure or vacuum; the fact that sealingsurface softness and conformability are limited; the fact that the useof more rigid plastics are not feasible; and the higher cost andcomplexity of mold construction and operation for a number of theproposed sealing designs.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a new andunique cap with a seal which develops and maintains a positive sealingpressure and engagement with a container opening throughout the shelflife of the contained product and upon opening and resealing thecontainer. The cap is substantially rigid and includes plastic materialand generally has a top wall or lid which covers the container opening.Preferably, the cap has a depending skirt which engages the finish of acontainer or bottle for opening and closing thereof. The seal is madefrom plastic and depends from the top wall of the cap. The sealpreferably is internally spaced from the peripheral skirt and includesan upper end depending from the top wall and a free end with a highlyresilient and compressible curled portion which preferably has arelatively soft and conformable sealing surface. As the cap is appliedto the container for closing, a curvilinear portion of the seal engagesthe container finish and readily compresses to provide a relativelylarge sealing area to seal the contained product. Preferably the cap islinerless with the seal integral with the top wall of the cap.

In a preferred embodiment, the linerless seal includes a substantiallyannular upper portion integral with and depending from the lid and asubstantially annular highly compressible curled free end which definesa hollow "O" or coiled ring. The hollowness of the curled "O" shape andrelative thinness imparts a high degree of compressibility as well asthe ability to recover from such compression. Additionally, the coiledconfiguration of the hollow "O" shape, which is affixed to the top wallof the cap at one end and free at its other end, imparts a furtherdegree of compressibility and recovery. Preferably the curled "O" shapeincludes an arc of from 270 to 360 degrees.

The compressibility of the hollow annular "O" ring is highlyadvantageous in its ability to adjust to neck dimension variations andout-of-round conditions prevalent in container or bottle manufacturingprocesses. The "O" ring shape of the seal not only accommodates to suchmanufacturing variability, but does so without excessive variations insealing pressure and associated capping, uncapping and sealingdifficulties. Because of the low variation in sealing pressure possiblewith the present invention, lower levels of sealing pressure may beemployed while maintaining an adequate minimum pressure to assure aproper seal. Such low sealing pressure allows the plastic material tooperate more within its elastic limits thereby contributing directly torelatively low loss of such pressure over long shelf life periods orthrough accelerated conditions, such as pasteurization processes, whichcause creep, i.e., plastic cold flow.

Also, because of the compressibility of the "O" rings shape, its sealingsurface can increase significantly resulting in improved seal integrity.This in turn allows lower sealing pressure and resulting sealingpressure losses as already noted.

Additionally, the high compressibility of the seal presents theadvantage of being able to use a single cap for different bottles of thesame nominal size and engagement means even though different bottlematerials (glass, various plastics) and associated neck bore diametersmay be used.

Another aspect of the present invention is the location of the curled orcurvilinear portion of the seal at or near the sealing contact area.Whether the curled portion is in the shape of an "O" ring, coil or othersimilar shapes, such as "U" or "J", this feature of the inventionenables the sealing surface to adjust to the container both radially andaxially. In turn, this contributes to lower localized stress anddeformation with the desirable result of lowering plastic creep.

In each of the foregoing embodiments of the integral seal of theinvention, whether it includes an "O" ring or other curl shape withinthe scope of the invention the seal includes a relatively large sealingarea and high levels of resilience, compressibility and resistance toplastic creep.

A further contribution of the invention toward maintaining sealingintegrity under use conditions comes from the extensive use ofcurvilinear cross sections in the seal supporting structure whichresults in more uniform distribution of sealing stresses over largerareas, including portions well removed from sealing contact, and theresultant reduction in localized stresses which cause localized plasticcreep.

Moreover, the integral seals of the invention can be a rim seal whichengages the top surface or rim of the neck finish, a plug seal whichabuts and seals the bore of the container neck, or a corner seal whichengages the rim and adjacent depending surface of the container neck. Ineach of the described seals of the invention, the curled portion canface outwardly or inwardly.

In another preferred embodiment, the stretched linerless seal preferablyhas balanced residual strain wherein the plastic at the sealing surfaceis in a state of tension and relatively soft and compressible and thesubstrate or supporting structure is in a balancing state of compressionand relatively hard and resistant to compression and which maintains thestate of tension and relative softness of the opposing sealing surface.

In yet another preferred embodiment the linerless sealing surface ismade relatively softer than the other cap portions as a result ofaltering it by stretching to produce microscopic voids employingplastics having this characteristic.

In another preferred embodiment, the linerless seal includes asubstantially annular upper portion integral with and depending from thelid and a substantially annular highly compressible curled lower portionwhich has a "J", "U", "O" or coiled cross section. Preferably the curledlower portion has a sealing surface which is softer than the rest of thecap as a result of its method of manufacture which includes stretchingit.

In forming the cap and integral seal of this invention, the cap isformed first by conventional molding techniques, such as injection orcompression molding, with an internal preform for the integral seal. Thepreform includes an annular wall which is spaced inwardly from theperipheral skirt and which is integral with and depends from the lid inan essentially vertical manner. Thereafter, the curled lower portion ofthe integral seal is formed by forming means which engage the wall toform and define the curved sealing surface and which stretches it toachieve the desired softnesss of preferred embodiments of the invention.

The curled lower portion is formed by a curling tool which engages thelower free end of the cylindrical preform, and turns it outwardly towardor inwardly from the skirt and then upwardly channeling and altering thedirection of such movement over its working surfaces. Preferably theinitiation of the curling action is facilitated by providing a taper tothe lower free end of the cylindrical preform. The curling action atthis point produces a "J" or "U" shape in such a free end. To produce an"O" or coil shape, after leaving the working surface of the tool, thefree end takes an upward and inward or outward direction relative toitself, which results from the continuing compression and the stressesimposed by its plastic memory, to complete the formation of a hollow "O"ring. Optionally, the compression of the cylindrical portion can proceedbeyond this point and produce a more fully coiled ring. The workingsurfaces of the curling tool are preferably curved but optionally aplurality of flat surfaces may be employed.

To facilitate the curling operation or to alter the dimensions, shape orcharacter of the resultant linerless seal, the curling tool can beheated and can be used in straight compression with, with or withoutspinning, or rolled along the free end of the cylindrical portion duringits shaping. The free end of the cylindrical portion may be curledsimultaneously or sequentially. Optionally, the linerless seal can beexposed to elevated temperatures for short periods before capping toalter its dimensions, shape or character or the preform for thelinerless seal can be heat treated for the same purpose.

The seal produced by the curling method of the present inventionincludes a relatively soft and conformable plastic sealing surface and asubstrate or supporting portion of the same plastic which is relativelystronger, more resilient and creep resistant. This is achieved byproducing and controlling strain within the plastic of the integral sealitself. Preferably the outer sealing surface of the seal is in a stateof tension while the inner or supporting substrate is in a state ofcompression. Optionally the cap may be made from a multiphase plastic ofthe invention so that the stretched sealing surface also includesresidual microscopic voids which soften it.

In another embodiment, the curled free end, where it contacts thedepending wall after formation of the O-ring shape, can be welded tosaid wall to form a sealed hollow space within resulting in a linerlessseal having pneumatic sealing qualities.

Another feature of the invention is that the curling operation of theinvention may be performed in sequence with or as part of other stepstaken in the manufacture of the cap. That is, it may be performed duringor consequent to removal from production molds or during or consequentto cap finishing operations such as lid decoration. It also can beperformed simultaneously with or consequent to a curling operation toproduce the tamper evident separable or breakaway ring of my copendingU.S. patent application, Ser. No. 809,057. Also the curling operationhas been demonstrated to be non-critical in respect to unusual controlor conditions so that automatic operation to produce uniform product canbe used to achieve high quality at low cost.

Another feature of the invention is that the cap and perform for theintegral seal are first produced in injection molds employing widelyaccepted and used mold design and technology. The simple shape of thecylindrical preform imposes no significant concern, limitation orexpenses in mold design and operation. Low cost molds employingtraditional stripper ejection mechanisms may be used because of theabsence of undercuts which otherwise could distort or tear. This alsoassures short cooling cycles in the mold.

Yet another feature of the invention is that relative height anddiameter of the curled seal is determined in a separate reformingoperation so that a single cap as molded, may be used to produce capswhich will fit a variety of bottle neck designs where dimensions, suchas thread or locking ring heights, wall thickness or internal diametervaries. The cost of the curling tools and the curling operation affectoverall cap cost very little, enabling the cap manufacturer to takeadvantage of the economies, of larger scale production for a number ofcustomers or user from fewer and larger production molds.

In addition, the curling methods of the present invention also canproduce linerless caps which include a relatively soft and conformablesealing surface of plastice and a substrate or supporting portion of thesame plastic which is relatively stronger, more resilient and creepresistant. This is achieved by the curling methods of the presentinvention which produce stresses in the plastic of the curled portion,wherein the stresses in the outer sealing surface are in a state oftension or extension and the stresses in the inner supporting substrateare in a state of compression. An additional feature is that, when usingpreferred plastics of the invention, softness of the sealing surface isfurther enhanced by the development of microscopic internal voidsproduced thereat by the method of the invention.

Additionally, because of the ease of cap ejection from the productionmold and because of the highly compressible "O" ring shape with itsattendant advantages for distributing applied stress, stronger and morerigid plastics can be used for performance or economic reasons.

In another embodiment of the invention as a plug seal, potentialblow-off of the cap during opening when used to contain products underpressure can be avoided by assuring that the seal comes out ofengagement with the container substantially before loss of the threadedor other attachment engagement. This can be accomplished without theconcurrent risk of distortion of the seal during capping which can occurin other designs which have narrow free ends and which employ suchserial engagement and disengagement of the sealing feature and threads.This advantage results from the full roundness of the bottom of the sealand its ability to adjust to cap-to-neck misalignment by movement in thehorizontal plane because of its curled shape and the relativedisplacement of its lid attachment and sealing planes.

Another embodiment of the invention is to locate the "O" ring shape sealor other shape having a curvilinear or curled sealing contact portion insuch a relationship to the rim of the bottle neck that upon itscompression by the neck during capping it forms a sealing surface on theinside corner of the rim and the surface adjacent to it on the neck rimand vertical wall. In this manner a very positive seal is achieved.

Another embodiment of the invention is to shape the seal into a "J"shape by abbreviating the extent to which the depending cylindrical capportion is curled, wherein the sealing surface is the curved or curledlower extremity and the attachment site to the lid is its upper annularextremity.

In another embodiment of the invention, the top surface of the bottleneck rim is employed for the sealing engagement using a cap having a "U"shape or semi-circular cross section integral seal, wherein one leg isattached to the cap lid and the other is unattached but adjacent the lidand optional restraint thereon while the lower curvilinear portionserves to provide the sealing surface. Such a shape can be wide enoughin relation to the neck thickness so that after torquing up the cap thehighly compressible "U" shape feature can overlap one or both edges ofthe neck rim. Also, the seal can be more fully curled so as to form an"O" ring shape or less fully curled to form a "J" or quarter-roundshape, wherein their lower curvilinear or curled portions engage theneck rim top surface.

In another embodiment, a quarter-round seal can be provided, wherein itsfree end is in engagement with coacting restraining means located on theinterior wall of the cap skirt while the curvilinear portion engages theexterior corner of the neck rim.

Still further, a more fully curled seal can be provided so that a coiledring is achieved which produces added resilience.

Moreover, the bottle neck rim can be produced with a concave surfacebetween its inside and outside walls to minimize ovaling of the curledseal to further reduce localized deformation and plastic creep.

In still another embodiment, the above described bottle neck rim can beused as the curling tool to postform the curled portion of the seal,thereby combining the curling operation with the capping operation.

In another embodiment of the invention the curled free end may behorizontally displaced from its opposite end which is integral with thetop wall by including a relatively straight or generally horizontalportion therebetween. This allows the o-ring seal of the invention tofloat and compress more freely, without a constraining influence fromthe portion of the seal which is fixed by its attachment to the topwall.

Another embodiment calls for the cap lid portion bounded by thelinerless seal to be made of a different material (e.g., metal, anotherplastic, etc.) with the curled free end itself used to engage the lidprior to capping and then used as well to seal the lid to the cap andthe cap to the container upon capping.

In another embodiment the curled free end of the linerless seal mayinclude radial slits away from the sealing surface so that theresilience of the curled free end may be enhanced.

An important feature of the invention is that it provides conformable,resilient, integral cap seals with superior ability to conform to theneck configuration of individual containers including those with typicalmanufacturing defects and aberrations.

Another feature of the invention is that it assures high sealingintegrity even when used with container necks having wide manufacturingdimensional tolerances.

Yet another feature of the linerless seal of the invention is that itprovides high sealing integrity over long shelf life periods withproducts which are pressurized or under vacuum and/or those subjected toelevated temperatures such as when pasteurized.

Another feature of the invention is the use of the seal forming methodto alter and enhance the physical properties of the plastic to provideoptimum sealing characteristics.

Another feature of the invention is that it can employ more rigidplastics than other linerless seal designs.

An additional important feature of the invention is its low costmanufacturing method using low cost molds and molding operations, fewerand larger molds and an integrated curling operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a description of the accompanying drawings ofillustrative embodiments of the invention. It is to be understood thatthe invention is capable of modification and variation apparent to thoseskilled in the art within the spirit and scope of the invention.

FIG. 1 is a top perspective view of a cap of the invention, partiallybroken away to show a preferred embodiment of the integral or linerlessseal;

FIG. 2 is a bottom perspective view of the cap of FIG. 1, also partiallybroken away to show the linerless seal;

FIG. 3 is a longitudinal sectional view of the cap of FIGS. 1 and 2after molding and with a preform for the linerless seal about to beengaged by a curling tool of the invention to produce an outward curlwhich provides the "O" ring seal shown in FIGS. 1 and 2;

FIG. 4 generally is the same as FIG. 3, except that the curling tool hasengaged the preform for the seal and initiated curling thereof;

FIG. 5 generally is the same as FIG. 3, except that the completedoutward curl of the linerless seal has been formed;

FIG. 6 is a longitudinal sectional view of the cap and "O" ringlinerless seal of FIGS. 1 and 2 ready for engaging the neck finish of abottle for closing the bottle and sealing the contained product;

FIG. 7 is the same as FIG. 6, except that the bottle has been closed andsealed by the cap and the linerless seal which is in the form of a plugseal;

FIG. 8 is an enlarged sectional view of the linerless seal and adjacentcap portion shown in FIG. 6 schematically illustrating the stresses inthe seal in the direction of the curl;

FIG. 9 is a graph schematically illustrating the balance of stressesillustrated in FIG. 8;

FIG. 10 is a stress strain graph for the stresses in the linerless sealshown in FIG. 8;

FIG. 11 is the same as FIG. 8, except the illustrated stresses are inthe hoop direction;

FIG. 12 is a horizontal plan view of the seal of FIG. 11;

FIG. 13 schematically illustrates what occurs to the seal of FIG. 11upon release of the hoop stress;

FIG. 14 schematically illustrates what occurs to the seal of FIG. 8 uponrelease of the stresses in the direction of curl;

FIG. 15 is a longitudinal sectional view of portion of a lid with adepending annular band prior to curling;

FIG. 16 is the same as FIG. 15, except that the annular band has beencurled with the resultant production of microscopic voids.

FIG. 17 is the same as FIG. 16, except that the curled free end is insealing engagement with the inside of a container neck and some of themicroscopic voids have been eliminated in the sealing area.

FIG. 18 is a longitudinal cross section of a cap and an optional curlingtool of the invention in early engagement with a preform for a linerlessseal of the cap.

FIG. 19 is generally the same as FIG. 18 except that the curling toolhas completed the formation of the O-ring linerless seal.

FIG. 20 is generally the same as FIG. 19 except that the curling toolworking surface is unitary.

FIG. 21 is a longitudinal cross section of a cap with a preform for alinerless seal positioned above a curling tool suitable for producing alinerless seal wherein the sealing portion is horizontally displacedfrom its lid attachment site.

FIG. 22 is generally the same as FIG. 21 except that the curling toolhas completed the formation of the horizontally displaced sealingportion.

FIG. 23 is a longitudinal cross section showing the cap of FIG. 22 insealing engagement with a container.

FIG. 24 is a longitudinal cross section of a cap including a separatelid portion prior to formation of an O-ring linerless seal including asealing engagement with the separate lid portion.

FIG. 25 is generally the same as FIG. 24 except that the O-ringlinerless seal has been formed and is in sealing engagement with theseparate lid portion.

FIG. 26 is a longitudinal section view of a portion of a cap linerlessseal preform in early engagement with a curling tool forming groovewhich has been modified to heat and melt the preform rim.

FIG. 27 is generally the same as FIG. 26 except that the tool curlingengagement has been completed and the preform rim has fused and beenwelded to an upper portion of the preform wall.

FIG. 28 is a longitudinal cross section of a portion of the linerlessseal of the invention which has been modified to have a plurality orslits to increase its resiliency during compressive sealing engagement.

FIG. 29 is a longitudinal sectional view of the slitting tool.

FIG. 30 is a plan view of the slitting tool of FIG. 29.

FIG. 30A is a cross sectional view of a portion of the curled seal ofFIG. 28, schematically illustrating the slitting by the blades of theslitting tool of FIGS. 29 and 30.

FIG. 31 is a longitudinal view of a snap cap with a preform for thelinerless seal about to be engaged by a curling tool of the invention toproduce an inward curl which provides an "O" ring linerless seal of theinvention;

FIG. 32 generally is the same as FIG. 31, except that the inward curl ofthe linerless seal has been completed;

FIG. 33 is a longitudinal sectional view of the completely formed snapcap of FIG. 32 snapped on the neck finish of a bottle to close and sealthe bottle;

FIG. 34 is a longitudinal sectional view of a threaded cap and linerlessseal of another embodiment of the invention in capping sealingengagement with a neck of a bottle, wherein the seal comprises an inwardcurl having an "O" ring shape;

FIG. 35 is a longitudinal sectional view of another embodiment of theseal of the present invention, wherein the seal generally has a "J" or"U" shape and is used as a plug seal;

FIG. 36 is a longitudinal sectional view of a cap and linerless seal ofstill another embodiment of the present invention, wherein the "O" ringis used as an interior corner seal;

FIG. 37 is a longitudinal sectional view of a portion of a capillustrating the sealing engagement between a linerless "O" ring seal ofthe present invention and the rim of the illustrated neck finish;

FIG. 38 is similar to FIG. 37, except that it illustrates the sealingengagement between a "U" shaped linerless seal of the present inventionand the rim of the illustrated neck finish;

FIG. 39 is a longitudinal sectional view of a portion of the cap andlinerless seal of another embodiment of the invention illustrating theuse of a coiled ring as a rim seal;

FIGS. 40 and 41 are longitudinal sectional views of a portion of the capand neck finish, illustrating the post-forming of a linerless seal ofthe invention by the neck finish during the capping operation;

FIGS. 42 and 43 are longitudinal sectional views of a portion of the capof the invention illustrating the post-forming of a corner seal by theillustrated curling tool;

FIG. 44 is a longitudinal sectional view of the cap and formed cornerseal of FIGS. 42 and 43 illustrating the sealing engagement of the sealwith a corner of the illustrated neck finish;

FIG. 45 is a longitudinal sectional view of a portion of a cap of theinvention showing the formation of a linerless corner seal of thepresent invention where the seal has a quarter-round shape;

FIG. 46 is a longitudinal sectional view of the cap and formedquarter-round linerless seal of FIG. 45 in sealing engagement with theexterior corner of the illustrated neck finish; and

FIG. 47 is a longitudinal sectional view of a portion of the capillustrating the postforming of the quarter-round linerless seal of FIG.45 by the neck finish during the capping operation.

FIG. 48 is a longitudinal sectional view of another embodiment of thecap of the invention including a preform for a tamper evident ring and alinerless seal within the cap ready for engagement by a curling tool ofthe invention.

FIG. 49 is the same as FIG. 48, except that the curling tool has fullyengaged the preform portions of the cap to form a linerless seal havingan O-shape cross section and an inwardly curled tamper evident ringhaving a J-shape cross section.

FIG. 50 is a longitudinal sectional view of the completely formed cap ofFIG. 49 engaging, initially closing and sealing the illustrated bottle.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 2, there is shown a semi-rigid, threaded,plastic cap 10, having a lid 12, a depending peripheral internallythreaded skirt 14 and an internal integral or linerless seal 16. Theillustrated integral seal 16 includes a cylindrical or annular verticalwall 18 having an upper end 20 integral with the lid 12 and a freecurved free end 22. As shown, the end 22 of the integral seal 16 iscurled outwardly and forms a hollow annular "O" or coiled ring 24.

Referring to FIGS. 3-5, there is shown a preferred method of forming thecurled portion 24 of the seal 16. In FIG. 3 the cap 10 already has beenformed by conventional molding techniques, such as injection molding,with a vertical cylindrical or tubular wall 18 having its upper end 20integral with the lid 12 and with its lower free end 22 ready forcurling by the illustrated curling tool 26. As shown in FIG. 3, there isa taper in lower end 22 extending from the rim 30 which facilitates theinitiation of the curl 24. The taper preferably extends from rim 30 fora distance sufficient to assure a full round curve to the curl 28adjacent its rim 30. For a typical curl 24 of the invention having awidth of 0.100 inches and a thickness of about 0.015 inches, the tapermay extend a distance of about 0.050 to 0.075 inches from the rim 30. Asshown in FIGS. 3-5, the free end 22 and the curl 24 are free of abruptchanges in thickness.

The curled portion 24 of the seal 16 is formed with a curling tool 26,which in FIG. 3 has been positioned within the cap 10 ready to engagethe preformed wall 18 at its lip or rim 30. The curling tool 26 includesa circular or annular groove 28 of a concave cross section suitable forshaping and dimensioning the curled portion 24.

As shown in FIG. 4, the forming operation is accomlished by pressing thegroove 28 of the tool 26 against the rim 30 of the wall 18. In thisembodiment the deepest portion 33 of the groove 28 representing thecenter of its concavity is located outwardly of the cylindrical plane ofthe wall 18. This is illustrated by the dotted lines 35 of FIG. 3. Alsothe groove 28 has a slanted portion 39 inwardly and tangent to itsconcavity to facilitate centering of the tool and cap. As movement oftool 26 relative to the wall 18 continues toward the lid 12, thecylindrical sides of the wall 18 are centered within groove 28 by theslanted portions 39 and are then forced outwardly and then upwardly toassume an interim "J" shape as shown in FIG. 4. As this relativemovement continues, the rim 30 is forced upwardly out of groove 28, andat the same time is pulled inwardly in response to the stressesdeveloped therein while being shaped by the tool 26, thereby producingthe desired "O" ring curl 24 with an attachment site 20 to the lid 12close to the plane of the inside diameter of its horizontal crosssection.

To facilitate the curling operation, in the case of polypropylene, thetool 26 may be at a temperature of about ambient to about 300 degrees F.but preferably about ambient to about 150 degrees F. for curling cyclesof about one-half to three seconds. Lower temperatures and shortercycles are preferred to maximize the desired strain of the inventionimposed by the curling operation on the plastic of the curl 24 asdiscussed hereinafter with respect to FIGS. 8 to 14.

After formation of the curl 24 the curling tool 26 is withdrawn from thecap 10 and the cap 10 is ready for capping and recapping. The "O" ringseal 16 includes a bottom sealing portion 32, an inside sealing portion34 and an outside sealing portion 36. Depending on whether a rim, corneror plug seal is desired one or more of these surfaces can be used forsealing engagement with the appropriate portion of a container or bottleneck. In each embodiment a curled or curved portion of the seal 16 isused as a sealing surface.

Referring to FIGS. 6 and 7 there is illustrated the use of the "O" ringlinerless seal 16 of FIGS. 1-5 as a plug type seal for a bottle 37(partially shown) having an externally threaded neck 38, a rim 40 and anopening or bore 42. As the cap 10 is threaded onto the bottle neck 38the curled bottom portion 32 of the seal 16 meets the interior annularcorner 44 of the rim 40 and the intersecting internal neck wall 46 whichforms the bore 42. Thereafter, the seal 16 seats itself within the bore42 with the external side sealing portion 36 in sealing engagement withthe wall 46 of the bore 42. This is accomplished because of the roundedbottom portion 32 and the ready compressibility of the "O" ring shape,wherein the compressed side sealing portion 36 of the ovalized seal 16forms a firm engagement with the wall 46 defining the bore 42.

A contribution to low localized stresses and low plastic creep by the"O" ring shape 24 of the invention lies in the fact that the curved sideportion 36 used for the sealing engagement with the neck inner wall 46lies between and is supported by both lower and upper curl portions 32and 29. In this manner the level of sealing stress transferred to eachsupporting portion is greatly lower then with only one supportingportion, typical of other linerless seals.

The side portion 36 adjusts to the constraint of wall 46 with resultantcompression, the stresses of which are transmitted to and distributedthroughout the "O" ring 24. The "O" ring 24 responds to such stress by areduction in both its external and internal diameters of its horizontalcross section in conjunction with an ovaling of its radial crosssection. For example, an "O" ring curl 24 having an external diameter of0.900 inch and an internal diameter of 0.707 inch when seated in thebore of a neck having an internal diameter of 0.846 inch produced animmediate reduction of 6 percent in its external diameter and areduction of 1.2 percent in its internal diameter, demonstrating asignificant distribution of sealing stresses throughout all portions ofthe "O" ring seal of the invention. Such extensive distribution ofstress throughout the "O" ring 24 derives from its hollow "O" ring shapeand the displacement of attachment site 20 from the sealing surface atthe side portion 36. This results in an advantageous reduction in stressconcentration and creep and the loss of sealing pressure over time whichcan result. Additionally there occurs an improvement in sealingengagement and integrity derived from flattening of the curved sideportion 36 as it adjusts to the constraint of the wall 46 whichincreases the sealing area. Also even though a large amount ofcompression occurs in the "O" ring 24, torque levels required to seatthe cap 10 and to remove it remain in a normal range.

The preferred curling method of the invention illustrated by FIGS. 3-5produces a linerless seal 16 which possesses the desired large sealingarea, a high level of resilience and elasticity and a high level ofresistance to plastic creep. In addition, the reforming method modifiesthe physical properties of the plastic in such a way as to furtherenhance its sealing characteristics. That is, the plastic at the sealingsurface of the seal 16 is made softer and more conformable and at thesubstrate and supporting portions is made stronger, more resilient andcreep resistant as a result of the stresses imposed on the plasticduring the curling operation. This enhancement will now be explained inconjunction with reference to FIGS. 8-14.

The curling operation, by imposing an alternative shape on the preformedcylindrical wall, imposes, it is believed, two sets of balanced residualstresses and stress differentials to the resultant shape in the seal 16.That portion of the seal 16 which is stretched is in extension or astate of tension and that portion which is compressed is in a state ofcompression. The level of stress varies with the degree of extension orcompression and, as in any static condition, the total amount anddirection of each kind of stress balances and maintains the other.

One set of balanced residual stresses occurs in the direction of curl asa result of the extension and compression of the preformed cylindricalwall 18 across its thickness to form the "O" ring or coiled ring shape24, as shown in FIG. 8. At and near the convex exterior surface (sealingsurface) represented by points B or Y the plastic is stretched in thedirection of the curl and is in a state of high residual tension. Theopposite concave interior surface, represented by points A or Z, iscompressed in the direction of the curl and is in a state of highresidual compression which balances and maintains the state of tensionat or near the exterior convex surface. FIG. 9 shows the direction, sumand approximate distribution of these stresses across the thickness ofthe plastic including the neutral point 0 and points of maximumcompression and tension at or near the inner and outer surfaces. In thenormal practice of the invention maximum tensile stress will occur overa finite distance from the surface. The sum of the compressive stressdefined by points AOC equals that of the tensile stress defined by thepoints BOD.

IN FIG. 10 there is shown a typical stress-strain curve for a semi-rigidplastic (e.g. polypropylene) suitable for the practice of the invention.The conditions of stress and elongation or compression in the directionof curl at points B and A in FIG. 8 are shown on the curve at typicallocations for the practice of the invention (preferably 50% of theelongation to yield and beyond and the corresponding level ofcompression). The dotted lines define that portion of the stress-straincurve wherein point B, representing the sealing surface of theinvention, will typically be found near to or well beyond the tensileyield point R. Also shown in FIG. 10 is a typical stress-strain curvefor a much softer plastic such as ethylene-vinyl acetate copolymers orpolyvinyl chloride plastisol which are popularly used for cap linersbecause of their soft conformable nature. When the portion of the curvefor the semi-rigid plastic defined by the dotted lines is compared tothe curve for the softer plastic, a similarity is noted wherein smallamounts of stress result in large amounts of deformation whichdemonstrates the desired softness, conformability and enhanced sealingqualities of the invention.

Thus, it can be seen that the curling process of the invention used tocreate the desired shape for superior sealing performance also modifiesthe physical properties of the plastic at the sealing surface from thoseof a more rigid, unyielding material suitable for overall cap strengthand integrity to those of a softer, more yielding and conformablematerial suitable for improved sealing characteristics.

From the location of point A in FIG. 10, it can be seen that the samecurling action which modifies the properties of the sealing surfacerepresented by points B or Y in FIG. 8 beneficially modifies theproperties of the supporting substrate represented by points A or Zoppositely, but also beneficially. Because the substrate at points A andZ is highly compressed, its strength and resiliency is maximized in thatthe amount that it can be deformed before any plastic or permanentdeformation occurs is significantly increased (proportional to the ratioof AE to OE of FIG. 10). These factors are highly beneficial towardsmaximizing the ability of the seal supporting substrate at point A togenerate the maximum amount of sealing pressure on its sealing surface(e.g., at point B) and to resist decay of such pressure over long timeperiods resulting from plastic creep.

At the same time, a second set of balanced stresses occurs normal to thefirst set as a result of the increase and/or decrease of the hoopdiameter of the cylindrical cap portion 18 of FIG. 3 when it ispostformed or reformed into the "O" ring 24 or other shape of the sealof the invention as shown in FIGS. 4 and 5. If it is considered that thecylindrical portion 18 is composed of an integrated stack of hoops, eachof which must be expanded radially (stretched) or compressed to producethe reformed shape, then a condition of tension or compression will beimposed on each of the hoops in the resultant shape as shown in FIGS. 11and 12 (respectively a radial cross section and a horizontal plan viewof the seal 16). The level of stress is relative to the amount the hoopshave been expanded or compressed and tension is highest at point Y,compression is highest at point X and hoop stresses are nil at theintermediate location of the original cylindrical preform 18, points Cand D.

Since two unidirectional sets of stresses operating normal to oneanother are imposed by the curling operation of the invention, theireffect on the various portions of the seal 16 are additive. Wheretension in the hoop direction is imposed at the same location as tensionin the curl direction (e.g., point Y), the plastic will further increasein softness and conformability. Where hoop compression is imposed at thesame location as tension in the curl direction (e.g., point X), theplastic will exhibit a lesser increase in softness, perhaps even adecrease in softness and an increase in strength and resiliency when thelevel of compression is higher than the level of tension. Where theplastic is in compression in both the hoop and curl directions (point Z)the greatest increase in strength and resiliency occur. At points C andD hoop stresses are nil so there is no additive effect. Therefore thedevelopment of a high state of tension in both the hoop and curldirection at point Y favors the use of the outwardly directed sealingsurface 36 in a plug type seal. The development of a high state oftension in the curl direction at point B favors the use of thedownwardly directed sealing surface 32 in a rim seal. The fact thatpoint X is in the lowest state of tension is not detrimental to thepractical application of the stresses of the invention since the insidesealing surface 34 is not ordinarily used. However, since this portionof the seal 16 serves to support the lower and outer sealing surfaces 32and 36, the high state of compression at point Z and throughout most ofthe seal wall at that location is highly beneficial. Thus, it can beseen that the distribution of stresses imposed by the curling operationof the invention is optimal for the highest performance of the seal 16resulting in enhanced softness and conformability of the plastic at thesealing surfaces 32 and 36 and in enhanced strength and resilience ofthe plastic of the substrate and supporting portions represented bypoints A and Z of the seal 16.

That the stresses described in the above analysis do in fact exist andare distributed in the manner described is demonstrated by annealingtests to observe the changes in shape which develop as such stresses arerelieved. For such a test 0.020 inch thick cylindrical walls 18 ofpolypropylene were curled in the manner of the invention to yield "O"ring shapes 24 having a ring outside diameter of 1.230 inches, insidediameter of 1.030 and a curl outside diameter of 0.100 inches. The "O"ring 24 was then split radially to facilitate the full release ofimposed stresses and then exposed to a temperature of about 300 degreesF., somewhat under the plastic's melting point, for five minutes. Underthese conditions the "O" ring 24 opened up in the hoop direction to aradius of 2.5 inches, a four-fold increase, demonstrating the presenceof very high levels of hoop stresses and hoop stress differentials. Atthe same time "O" ring 24 opened up in the curl direction to a radius ofabout 0.150 inches, a three-fold increase, demonstrating the presence ofvery high levels of stresses and stress differentials in the directionof the curl. These results illustrated in FIGS. 13 and 14, demonstratethe conclusion drawn by the preceding analysis of the contribution ofthe stresses imposed by the curling operation to the development of thehigh levels of sealing integrity of the invention through the alterationand enhancement of the physical properties of the plastic used tomanufacture the cap 10.

Referring to FIGS. 15 to 17, there is shown a feature of the inventionwherein the sealing surface is softened as a result of the production ofmicroscopic voids thereat by employing plastics which form such voidsafter stretching. FIG. 15 shows the wall 18 integral with lid 12 andincluding free end 22 prior to curling. FIG. 16 shows the curled freeend 24 including microscopic voids 25 produced during the curlingoperation which preferably is done at ambient temperatures to facilitatethe creation of the voids 25. The size and/or number of the voids 25 arein relationship to the degree to which the plastic has been stretched.FIG. 16 shows that the void formation is greater where the plastic hasbeen stretched most in the hoop direction at the outside sealing portion36 while lower surface 32 and upper surface 29 possess microvoidsprimarily as a result of stretching in the curl direction. FIG. 17 showsthe seal 16 employed as a plug seal against the interior neck wall 46and the compression of the outside sealing portion 36 by the sealingengagement with the resultant elimination of the voids in the seal area.

Another feature of the invention is that from a single design of moldedcap and seal preform, the kind of seal and its dimensions can be variedto adapt to a variety of bottle neck dimensions and bottle materials.For instance, a molded cap with a cylindrical preform suitable to beused for a plug seal for a plastic bottle can also be used to produce arim seal for the same or other plastic bottle or a rim seal for a glassbottle simply by employing alternate curling tools. In the same mannerthe seal height for a rim seal can be readily altered in the curlingoperation to permit its use on bottles having a variety of threadheights. In this manner a single injection mold can be used to producecaps to fit a variety of bottle dimensions producing economies of scalein the cap molding and manufacturing operation.

Still another feature of the invention is that the caps and linerlessseals of the invention can be removed and unsealed without blow-off whenthe contents of the container are under pressure. For example, in a plugseal of the invention the distance between the under part of lid 12 andthe sealing engagement of outside sealing surface 36 should equal nomore than 1/2 the pitch of the cap threads--so that at least 1/2 turn ofthread engagement remains after the outside sealing surface 36 clearsthe inside wall 46 of the bore 42 during uncapping. For most caps thisdimension would be about 0.060 to 0.090 inches. In a rim seal the amountof elastic compression of seal 16 should be no more than 1/2 the pitchof the cap threads--so that at least 1/2 turn of thread engagementremains after the lower sealing surface 32 of seal 16 clears the rim 40of bottle neck 38. This dimension also would be expected to rangetypically between 0.060 to 0.090 inches.

In the case of a 28 mm polypropylene cap typical dimensions of the "O"ring curl 24 of seal 16 are about 0.040 to 0.150 inches for the curldiameter and about 0.007 to 0.030 inches in wall thickness and theradial cross section preferably forms an arc or a continuous curve of atleast 180 degrees. As a plug seal it typically will have an outsidediameter at its sealing surface 36 which is 0.020 to 0.060 inches largerthan the inside wall 46 of neck 38 with larger ranges applicable tolarger size caps. Preferred dimensions for the curl 24 to providemaximum plastic property enhancement through imposed stresses bypractice of the present invention call for maximum wall thickness andminimum curl diameter low curling temperatures and high curling speed.

Cap sizes typically range from under 20 mm to 120 mm and bottle and/orjar sizes range from under 2 ounce to 128 ounce capacity. Largercapacity containers such as drums or kegs are also suitable for thepractice of the invention as are smaller vials and other containers.

Useful plastics which can be used for forming the caps and linerlessseals of the invention include polypropylene, polyethylene, polystyrene,acrylonitrile-styrene-butadiene polymers, and many other semo-rigid torigid plastic materials. Optionally other plastics employed in thepractice of the invention are chosen from the group of plastics whichhave in common the fact that when stretched beyond their tensile yieldpoint they develop microscopic voids or fissures within the plasticwhich serve to soften it and make it more compressible, even whenresidual tensile strain is not present. The group of plasticsmanifesting this behavior includes essentially all polymer classes(e.g., polystyrene, polyvinyl chloride, polyolefins, polycarbonates,polysulfones, polyesters, nylons, etc.) and preferably are selected fromthe group of plastics known as alloys, blends, multipolymers, multiphasepolymers or other nomenclature, many of which are listed in ModernPlastics Encyclopedia, 1986-1987, pages 105 to 111, the entiredisclosure of which is incorporated herein by reference. Examples ofsuch polymers are propylene copolymers (e.g., Shell 7522),ethylene-propylene copolymers (e.g., Himont SB781) and rubber modifiedpolysytrene (e.g., Monsanto Lustrex 4300). Typically the Shell 7522propylene copolymer produces voids in the range from about 0.25 micronsto about 3.0 microns.

The linerless seals of the present invention can be used in a widevariety of caps including combinations with other materials (e.g., capshaving metal lid portions or portions utilizing different plastic thanthat used for the seal). Such linerless seals may be used to close andseal a wide variety of containers for a wide variety of productsincluding: beverages, including carbonated soft drinks and pasteurizedbeverages such as beer; foods, especially those where container sealingperformance is critical, including oxygen sensitive ones such asmayonnaise, peanut butter and salad oil, and including corrosive onessuch as vinegar, lemon juice; and household chemicals, includingbleaches and detergents, drugs and cosmetics and other productsrequiring the highest integrity seal and reseal under the widest rangeof distribution and use conditions.

Further, the linerless seals of the present invention can be used inconjunction with other types of linerless seals including other typeseals of the invention and may employ various or all surfaces of theneck 38. Moreover, the linerless seals of the present invention can beused with a wide variety of caps, including snap caps and threaded capswith or without breakaway rings. Specifically, the linerless seals ofthe present invention can be used with the caps having the breakaway orseparable rings disclosed in my U.S. Pat. No.: 4,709,824.

Referring to FIGS. 18-20, there is shown another method of the inventionfor forming the curled portion 24 of the seal 16, wherein the curl istighter and stretching is greater relative to FIGS. 1 to 7. FIG. 18shows the tubular wall 18 has been engaged and turned outwardly by toolcomponent 56a to form a horizontal wall portion 18a. The outwardhorizontal direction of the wall portion 18a upon compression by toolcomponent 56a is assured by an outwardly directed bevel to the free end22 at rim 30. Optionally the top surface of interior tool component 56amay be beveled outwardly or wall 18 may be molded with a conical oroutwardly flaired free end to assure the outward direction of wallportion 18a. FIG. 19 shows how the horizontal wall portion 18a is turnedupwardly to produce the relatively tight U-shaped curl 24 by suitablyinterrupting the travel of tool component 56a and continuing the travelof tool component 56b. After being turned upwardly the free end 30 ofwall 18 turns inwardly in a tight curl as a result of the stressesimposed by its plastic memory. The curled ring 16, produced by thismethod, can be a "J", "U" or quarter-round shape by employing suitabledimensions for wall 18 or tool 56 and/or by adjusting the amount ofcompression of wall 18 by tool 56. The cessation of travel of toolcomponent 56a relative to tubular wall 18 and tool component 56b may beabrupt, but preferably it is gradual to facilitate formation of atightly curled ring 16. Preferably the preform wall 18 is vertical wherethe curled portion 24 is produced to achieve the maximum appliedcurvature and the greatest degree of stretching and softening.

Optionally, the tool 56 may be unitary as shown in FIG. 20 or the toolcomponents 56a and 56b may be employed to do their respective portionsof the curling operation at separate work stations. Another option is toproduce the curled free end 22 inwardly by suitable alteration of thetaper of the wall free end 22 and the dimensions and sequence ofoperation of tool components 56a and 56b. As illustrated the curl of theembodiment of FIG. 20 is not as tight as shown in FIG. 19. In thisinstance the vertical component 56b is spaced further away from thedepending wall 18 then the corresponding vertical component 56b of FIG.19. Thus, by this method the tightness of the curl is readilyadjustable.

Referring now to FIGS. 21 to 23, there is shown another embodiment ofthe invention in which the curled free end 24 is horizontally displacedby a generally flat portion 48 from the attachment site of upper end 20to the lid 12. In this manner the curled free end 24 is completely freeto be compressed when used as a rim seal without the reinforcinginfluences of upper end 20 on its compressibility. FIG. 21 shows the cap10 as molded, positioned above curling tool 27 prior to curling. Thecurling tool 27 has a groove 28 including a beveled portion 39, a flatportion 41a and a curved portion 41b. Under compression from tool 27,the cap free end 22 enters the groove 28 at the beveled, lead-in portion39, travels outwardly along the flat groove portion 41a until it iscurved upwardly by curved portion 41b whereupon it continues to curlupwardly and inwardly as a result of its plastic memory. Optionally theupward and inward curling can be facilitated by shaping the bottom oflid 12 to form a groove 11 to receive and help shape the free end 22.FIG. 23 shows the curled free end 24 in compressive sealing engagementwith rim 40 of bottleneck 38 wherein the upper end 20 is displaced fromthe area of sealing engagement. Optionally the curled free end 24 may belocated inwardly from the upper wall portion 20 employing suitablemodifications of tool 27.

Referring now to FIGS. 24 and 25 there is shown a threaded cap of theinvention including a separate lid. FIG. 24 shows a cap 10, as molded,including a lid 12 having a a central opening 13 bounded by a dependingwall 18 with an upper portion 20 and a free end 22. The central opening13 is bounded at the lid 12 upper surface by an inward projection 15.Located in the opening 13 is a metal lid portion 50 which abuts the lidinward projection 15 and is bounded by upper wall portion 20. FIG. 25shows the cap 10 with its metal lid portion 50 after the wall 18 hasbeen curled by the method of the invention as shown in FIGS. 3 to 5except that the curled portion 24 is inwardly directed so as to fixedlyengage the metal lid portion 50 in a sealing engagement. The cap 10 isnow ready for capping a container and the curled portion 24 of itslinerless seal 16 performs a sealing engagement on both the containerneck and the cap metal lid portion 50. Optionally the central lidportion 50 may be made of other materials such as plastic which offertransparency, barrier, cost or other advantages.

Referring now to FIGS. 26 and 27 there is shown another embodiment ofthe invention wherein a hollow shaped ring is formed and welded toenclose a hollow space thereby creating an article having pneumaticqualities. FIG. 26 shows a wall 18 with its free end partially curled bya tool 26. The tool 26 includes an annular groove 28 a portion of whichis bounded by an annular tool insert 52 for heating at a hightemperature and an insulating portion 51 to allow the remainder of tool26 to be operated at a lower temperature. The free end 22 has a rim 30which has a reduced thickness which can be heated to a meltingtemperature more quickly than the remainder of free end 22. The heatedtool insert 52 is heated to a temperature sufficiently above the meltingpoint of the plastic to melt the rim 30 of reduced thickness but nothigh enough to melt the thicker succeeding portions of free 22 as itpasses in contact with it during curling to form an O-shape 24 of freeend 22. When the melted rim 30 completes its curling it contacts thewall 18 and forms a welded attachment 19 therewith as shown in FIG. 27.The resultant curled free end 24 is thereby prevented from anypossibility of being uncurled as well as converted into a pneumaticshape. Optionally the curled free end 24 may be welded or otherwisebonded by other means after the O-shape cross section has been formed.

Referring now to FIGS. 28 to 30A there is shown another embodimentwherein a non-sealing portion of the linerless seal 16 of the inventionis slit radially to provide enhanced resilience during a compressivesealing engagement. FIG. 28 shows a cross section of an inwardly curledfree end 24 showing a slit 54 on its inner portion 34. The slits servethe purpose of eliminating the hoop strength of inner portion 34 so thatresistance to compression occurs primarily in the curl direction. FIGS.29 and 30 show a slitting tool 58 with slitting elements 59 spacedradially about its upper periphery. To produce the slitted linerlessseal 16, the curled free end 24 is first produced by the methoddescribed in FIGS. 3 to 5 and then the slitting tool 58 is brought intoengagement with it to produce the slits (see FIG. 30A). Optionally theslitted curled free end may be produced having an outward orientation.Also the slits may be produced to extend to the lip 30 after curling orby slitting the wall 18 prior to curling.

Referring now to FIGS. 31 to 33, there is shown a snap cap 10 and anintegral plug seal 16a wherein the curl 24a is formed by curling tool 26inwardly and upwardly so that the outside sealing surface 36 iscontiguous with the upper end and attachment site 20 of seal 16a. Theinward direction of the curl 24a is achieved by locating the center ofconcavity 33 of the curling groove 28 inwardly of the cylindrical planeof wall 18 as illustrated by the dotted lines 35 of FIG. 31. In thisembodiment to develop the maximum compressibility and adaptability ofseal 16a to the neck wall 46, the plane of attachment site 20 must bedisplaced as much as possible from the plane of the neck wall 46.Therefore, it is necessary to develop the maximum curvature to theoutside sealing surface 36 which is now contiguous to the attachmentsite 20. This is accomplished by locating the center of concavity 33 ofgroove 28 as close as possible to the plane of wall 18, which isfacilitated by tapering the lower free end 30 of wall 18 away from thecenter of concavity 33 and by removing any restraints to the freeoutward displacement of surface 36 resulting from the stresses imposedduring the curling operation by providing ample free space in theoutward slanted portion 39 of groove 28. This results in lcoating theplane of sealing surface 36 further from the attachment site 20 as shownin FIG. 33. Preferably the radial cross section of the curled portion ofseal 16a includes an arc or curved portion of from about 90 to about 450degrees.

In FIG. 34, there is shown a threaded cap 10 and integral plug seal 16bwherein the curl 24b has been formed by a curling tool 26 (not shown)inwardly and upwardly. As a result, the hollow interior 48 of the "O"ring is in communication with the interior of the partially showncontainer 37. In this manner internal pressure 50 (indicated by arrows)within container 37 is directed toward the inside surface 52 of sidesealing portion 36 thereby using this pressure to reinforce the sealingengagement developed by the forced fit of the seal 16b within the wall46 of the bore 42. Thus, the internal pressure 50 acting to separate thesealing portion 36 from the wall 46 at their interface is offset by thesame pressure 50 acting to force the sealing portion 36 against the wall46 of the bore 42. This embodiment of the invention has particularadvantages for containers holding pressurized products.

FIG. 35 illustrates an embodiment of the invention wherein the integralseal 16c has a "J" shaped curl which is formed as shown in FIG. 4. Theseal 16c is used as a plug seal in sealing engagement with the wall 46of the bore 42 of the bottle neck 38. The J shape seal 16c possesses theadvantages of the present invention including the curled or curvilinearside sealing portion 36, a bottom curled portion 32, and substantialinward displacement of the attachment site 20 from the sealing surfacesbetween the curled side portion 36 and wall 46. In this embodiment thesealing stresses are distributed over the bottom portion 32 having ahalf round or semicircular cross section so that localized stress levelsand plastic creep may be higher in comparison with the "O" ringembodiment of the invention, but still well within the desired improvedperformance of the invention. Preferably the radial cross section of thecurled portion of the seal 16c includes an arc of about 90 to 180degrees.

In FIG. 36 there is shown a "O" ring integral seal 16d which is similarto the seal 16 of FIGS. 5 to 7 but with a larger diameter so that whenthe cap 10 is applied to the bottle neck 38, the seal 16d will not seatitself completely within the bore 42 but will be compressed by theinterior corner 44 of the neck rim 40 in such a way as to provide asealing engagement at corner 44 and its adjacent surfaces on rim 40 andthe wall 46 of the bore 42. Such a sealing engagement employs the highcompressibility of the hollow "O" ring 24d advantageously to enhance theseal integrity of the seal 16d by providing large sealing areas on therim 40 and wall 46 in addition to a high localized sealing pressure atthe corner 44 while retaining much of the resilience contributed by itscurvilinear cross section and freedom to float in the horizontal plane.

In FIG. 37 the "O" ring seal 16e is similar to seal 16 shown in FIGS. 5and 7 and seal 16d shown in FIG. 36 except that its larger diameter inthe horizontal plane positions it directly above bottle neck rim 40where it is employed as a purely vertical compressive seal using theadvantageous hollow "O" ring shape 24e. A recess 53 is provided in lid12 above "O" ring 24e to closely conform to its convex exterior surface.As a result, the performance of seal 16e is similar to that of seal 16except that its sealing engagement is with rim 40, it does not move inthe horizontal plane and, where desired, sealing pressures can beincreased to much higher levels depending on the level of torque appliedduring capping.

In FIG. 38 the seal 16f is formed into a semi-circular or U shape 24f.This shape is produced in the same manner as the "J" shape 16c asillustrated in FIG. 4 except that the vertical leg of wall 18 iseliminated. Bumpers 54 and 56 have been incorporated into the undersideof lid 12 to fix the lip 30 into position and to restrain its movementduring use. The performance of seal 16f compares to the "O" ring shapeof seal 16e of FIG. 37 in most respects except that its smaller crosssection yields a higher level of stress concentration and plastic creep,although well within the desired improved performance levels of theinvention. Optionally, bumber 54 may be extended in height to providefurther reinforcement to lower portion 32 of seal 16f and a positivestop to its compression during sealing engagement.

FIG. 39 illustrates a linerless seal 16g having an "O" ring shape with ahighly coiled cross section 24g which abuts a concave surface 53 locatedin lid 12. In sealing engagement the seal 16g also abuts a concavesurface 58 located on the neck rim 40. The seal 16g is produced by morefully curling the "O" ring shape of seal 16e of FIG. 37. The concavesurfaces 53 and 58 are dimensioned to conform to the curvature of thecurl 24g of seal 16g so that when the cap 10 is torqued up duringapplication to the neck 38, the seal 16g is restrained from therebyovalizing and therefore more fully translates the compressive sealingstresses into the further coiling of feature 16g. As a result, thecompressive sealing stresses are even more uniformly distributed thanwith seal 16e of FIG. 37 with resultant enhanced creep resistance andmaintenance of seal integrity.

FIGS. 40 and 41 illustrate an embodiment of the invention wherein thebottle neck 38 of FIG. 39 with its concave surface 58 can be used tocurl the as-molded preform cylindrical wall 18 of the cap 10 shown inFIG. 3. In FIG. 40 the wall 18 is as molded (preformed) with concave rim58 of the bottle neck 38 ready to engage and curl the wall 18 as the cap10 is applied. FIG. 41 shows the results of fully seating the cap 10onto bottle neck 38 with the downward thrust of wall 18 into the concavesurface 58 resulting in a seal 16h of the invention having an "O" ringshape 24h.

FIGS. 42 to 44 illustrate the formation and sealing engagement of an "O"ring 24j of the invention on the underside of the cap lid 12 in such away as to engage the exterior annular corner 60 of the neck rim 40.

In FIG. 42 the curling tool 26 includes an annular forming groove 31alocated at its top outermost location with transitional seal 16i curledoutwardly and slightly upwardly. As the end 30 of the transitional shape24i leaves forming groove 31a, it is directed both outwardly andupwardly resulting in a completed "O" ring shape 24j which extendsbeyond the perimenter of curling tool 26 well into the interior corner63 of cap 10, as shown in FIG. 43. In this location it will engage theexterior corner 60 and the contiguous rim 40 and depending surface 64 ofbottle neck 38 in sealing engagement as shown in FIG. 44. Theperformance of the seal 16j compares in many ways to that of seal 16d ofFIG. 36.

FIGS. 45 and 46 illustrate the use of a quarter round curled seal 16k ofthe invention restrained at its free end to increase its sealingstrength and to distribute its sealing stresses more uniformly.

FIG. 45 shows the quarter round seal 16k is curled to engage and berestrained by a shelf 66 in the interior wall of the cap skirt 14. Asshown in FIG. 46, engagement by exterior or outer corner 60 of the neckrim 40 compresses the seal 16k. In doing so the sealing stresses areresisted by both the attachment site 20 and the engagement of rim 30 andshelf 66. As a result, the stresses are more uniformly distributed.Preferably the radial cross section of the curled portion of the seal16k includes an arc of about 60 to 90 degrees.

FIG. 47 illustrates how the bottle neck 38 can be used to postform thequarter round seal 16k of FIG. 45. In this embodiment the outer corner60 of neck 38 has a beveled, slightly concave surface to engage end 30of the preform wall 18 (not shown) during capping. FIG. 47 shows theresults of fully seating the cap 10 onto bottle neck 38 with thedownward thrust of wall 18 onto the beveled outer corner 60 resulting ina seal 16k of the invention having a quarter round shape 24k.Optionally, the inner corner 44 of the bottle neck 38 may be similarlybeveled and shaped to engage and curl the preform wall 18 during cappingto form a modified plug seal.

FIGS. 48 to 50 are illustrative of how the curling operation of theinvention can be combined with the curling operation of my copendingapplication U.S. Pat. No. 4,709,824 to concurrently form the linerlessseal of the present invention and the breakaway ring of the invention ofmy copending application.

As shown in FIG. 48, the cap 10 is molded with a line of weakness 17including bridges 66 and a depending tubular band 68 as well as with thepreforms annular wall 18 depending from the lid 12 for an internalintegral or linerless seal 16. The wall 18 includes an upper end 20integral with the lid 12 and a depending free end 22.

In the illustrative embodiment, the curling tool 80 has an upper portion26 with an annular groove 28 for forming an inward curl in the free end22 and a lower portion 82 having an annular groove 84 for forming aninward curl in the free end 72. As illustrated, the tool upper portion26 is positioned within the annular groove 84, extends upwardly, and hasa diameter which is less than the diameter of the cap 10 so that it canextend thereinto to form the linerless seal 16.

In FIG. 48 the tool 80 is positioned below and within the cap 10 readyto engage simultaneously the outer and inner tubular walls 68 and 18.FIG. 49 shows the curling tool 80 fully engaged with cap 10 havingcompleted the formation of an "O" ring curl 24 to produce linerless seal16 and a breakaway ring 76. In this embodiment the wall 68 is curled toa lesser extent than for the "O" ring curl 24 of the linerless seal 16by stopping the curling compression at the appropriate stage. Thisresults in a "J" shape for the ring 76 which engages locking ring 41 ofbottle neck 38 as shown by FIG. 50. At the same time the linerless "O"ring seal 16 is a plug seal which engages and seals against the wall 46of the bottle opening 42 in the neck 38 thereof.

The invention in its broader aspects is not limited to the specificdescribed embodiments and departures may be made therefrom within thescope of the accompanying claims without departing from the principlesof the invention and without sacrificing its chief advantages.

I claim:
 1. A cap for a container, comprising:a top wall and a walldepending from said top wall within the cap comprising plastic andhaving a stretched, sealing surface which is softer than contiguousunstretched portions and which upon engagement with a container isadapted to compress and seal.
 2. A cap as defined in claim 1, whereinsaid sealing surface is stretched into cross-sectional shape selectedfrom the group consisting of a coli, O, U, J, or quarter round.
 3. A capas defined in claim 1 wherein said sealing surface is stretched so thatits soft sealing surface is in a state of tension.
 4. A cap as definedin claim 1 wherein said plastic is selected from a group consisting ofpolymers which when stretched produce microscopic voids that soften andmake plastic more compressible, and said plastic being prestretched toprovided a pre-stretched, pre-softened linerless sealing surface whichincludes microscopic pores.
 5. A cap as defined in claim 1 wherein saidtop wall of the cap includes a groove laterally spaced from thedepending wall at the top wall for receiving the sealing surface.
 6. Acap as defined in claim 1 wherein said sealing surface curled inwardly.7. A cap as defined in claim 1 wherein said sealing surface is curledoutwardly.
 8. A cap as defined in claim 1 which is a twist cap.
 9. A capas defined in claim 1 which is a snap cap.
 10. A cap as defined in claim2 wherein said sealing surface is a plug seal, a top seal or a cornerseal.
 11. The cap of claim 1 in combination with a container.
 12. Acombination as defined in claim 11 wherein said container is glass. 13.A combination as defined in claim 11 wherein said container is plastic.14. A plastic seal for a container, comprising a pre-stretched andpre-softened linerless sealing surface which includes microscopic voidsand which is adapted to compress and seal upon engagement.
 15. A seal asdefined in claim 14 wherein said sealing surface is stretched into across-sectional shape selected from the group consisting of a coil, O,U, J, or quarter round.
 16. A seal as defined in claim 14 wherein saidsealing surface is in a state of tension.
 17. A linerless cap for acontainer, comprising:a top wall, and a depending wall within the capintegral with and extending from said top wall to a free end, whereinsaid free end is curled into a compressible and resilient,pre-stretched, pre-softened, linerless sealing surface and wherein saiddepending wall adjacent said seal is angularly sloped and laterallydisplaces said seal from the point the depending wall depends from thetop wall.
 18. A cap as defined in claim 17, wherein said top wallincludes a groove for receiving said curled seal.
 19. A cap as definedin claim 17 wherein said end is curled into a cross-sectional shapeselected from the group consisting of a coil, O, U, J, or quarter round.20. A cap as defined in claim 17 wherein said end is stretched so thatits soft sealing surface is in a state of tension.
 21. A cap as definedin claim 17 wherein said sealing surface is curled inwardly.
 22. A capas defined in claim 17 wherein said sealing surface is curled outwardly.23. A cap as defined in claim 17 wherein said sealing surface is a plugseal, a top seal or a corner seal.
 24. The cap of claim 17 incombination with a container.
 25. A combination as defined in claim 24wherein said container is glass.
 26. A combination as defined in claim24 wherein said container is plastic.
 27. A cap for a container,comprising:a top wall with a central opening therein a lid below saidopening, and a depending wall adjacent said opening integral with andextending from said top wall to a free end of plastic curled intoholding and sealing engagement with said lid.
 28. A cap as defined inclaim 27 wherein said end is curled into a cross-sectional shapeselected from the group consisting of a coil, O, U, J, or quarter round.29. A cap as defined in claim 27 wherein said end is stretched so thatits soft sealing surfaces is in a state of tension.
 30. A cap as definedin claim 27 wherein said depending wall is a plastic selected from agroup consisting of polymers which when stretched produce microscopicvoids that soften and make plastic more compressible, and said plasticincreases stretching to provide a pre-stretched, pre-softened linerlesssealing surface which includes microscopic pores.
 31. A cap as definedin claim 27 wherein said curled free end of said wall also is acompressible and resilient seal adapted to be engaged for sealing.
 32. Acap as defined in claim 31 wherein said is curled inwardly.
 33. A cap asdefined in claim 31 wherein said is curled outwardly.
 34. A cap asdefined in claim 31 wherein said sealing surface is a plug seal, a topseal or a corner seal.
 35. The cap of claim 27 in combination with acontainer.
 36. A combination as defined in claim 35 wherein saidcontainer is glass.
 37. A combination as defined in claim 35 whereinsaid container is plastic.
 38. A linerless cap for a containercomprising:a top wall, and a depending wall within the cap comprisingplastic and having an end integral with and extending from said topwall, and a lower curled free end extending away from said dependingwall having a cross-sectional shape of an O ring terminating in a rim incontact with and welded to said depending wall and which is apre-stretched, pre-softened, linerless sealing surface.
 39. A cap asdefined in claim 38 wherein said end is stretched so that its softsealing surface is in a state of tension.
 40. A cap as defined in claim38 wherein said depending wall is a plastic selected from a groupconsisting of polymers which when stretched produce microscopic voidsthat soften and make the plastic more compressible, and said plasticbeing pre-stretched to provide a pre-stretched, pre-softened linerlesssealing surface which includes microscopic pores.
 41. A cap as definedin claim 38 wherein said sealing surface is curled inwardly.
 42. A capas defined in claim 38 wherein said sealing is surface curled outwardly.43. A cap as defined in claim 38 wherein said sealing surface is a plugseal, a rim seal or a corner seal.
 44. The cap of claim 38 incombination with a container.
 45. A combination as defined in claim 44wherein said container is glass.
 46. A combination as defined in claim44 wherein said container is plastic.
 47. A linerless cap for acontainer, comprising:a top wall, and a seal within the cap including adepending wall having an end integral with and extending from said topwall to a lower curled free end comprising plastic and extending awayfrom said wall to provide a curved sealing portion prior to engagementand which upon engagement is adapted to compress and seal, said curledfree end including slits in the non sealing portion of said curled freeend.
 48. A cap as defined in claim 47 wherein said seal is stretchedinto cross-sectional shape selected from the group consisiting of acoil, O, U, J, or quarter round.
 49. A cap as defined in claim 47wherein said seal is in a state of tension.
 50. A cap as defined inclaim 47 wherein said plastic is pre-stretched and pre-softened toprovide a linerless sealing surface.
 51. A cap as defined in claim 47wherein said end is curled into cross-sectional shape selected from thegroup consisting of a coil, O, U, J, or quarter round.
 52. A cap asdefined in claim 47 wherein said end is stretched so that its softsealing surface is in a state of tension.
 53. A cap as defined in claim47 wherein said depending wall is a plastic selected from a groupconsisting of polymers which when stretched produce microscopic voidsthat soften and make plastic more compressible, and said plastic beingpre-stretched to provide a pre-stretched, pre-softened linerless sealingsurface which includes microscopic pores.
 54. A cap defined in claim 47wherein said seal is a plug seal, a rim seal or a corner seal.
 55. Thecap of claim 47 in combination with a container.
 56. A combination asdefined in claim 55 wherein said container is glass.
 57. A combinationas defined in claim 55 wherein said container is plastic.
 58. Alinerless tamper evident cap, comprising:a top wall, an outer dependingskirt with a line of weakness and a curled free end of plastic forinterfering engagement with a container upon capping so that uponinitial removal of the cap the line of weakness separates to indicatethe condition of the container, and an inner depending wall integralwith and extending from said top wall to a curled resilient andcompressible plastic free end adapted to be engaged by the container forsealing upon capping and closing.
 59. A cap as defined in claim 58wherein said end is stretched into a cross-sectional shape selected fromthe group consisting of a coil, O, U, J, or quarter round.
 60. A cap asdefined in claim 58 wherein said inner depending wall free end is in astate of tension.
 61. A seal as defined in claim 58 wherein said plasticof said inner depending wall free end is pre-stretched and pre-softenedto provide a linerless sealing surface.
 62. A cap as defined in claim 58wherein said inner depending wall is a plastic selected from a groupconsisting of polymers which when stretched produce microscopic voidsthat soften and make the plastic more compressible, and said plasticbeing pre-stretched to provide a pre-stretched, pre-softened linerlesssealing surface which includes microscopic pores.